V.A. Elterman, L.A. Yolshina, P.Yu. Shevelin, A.V. Borozdin.
ABSTRACT
Chloraluminate ionic liquids are the most promising electrolytes for low-temperature electrolysis of aluminum and aluminum-ion batteries. An urgent problem in this area of research is the determination of the ionic composition and concentration of ions in IL. In this work, we investigated a low-temperature melt of the composition AlCl3–1-butyl-3-methylimidazolium chloride in the acidic range of aluminum chloride concentrations (at molar fractions of aluminum chloride from 0.5 to 0.67). To calculate the molar concentrations of ions in the electrolyte under study, a cycle of measurements of the density of the ionic liquid by the dilatometric method was carried out in a wide temperature range (from 0 to 100°C). From the experimental density values, the molar volumes of the ionic liquid were calculated. Isotherms and polytherms of the density and molar volume of the ionic liquid are linear. With increasing temperature, the density of the ionic liquid decreases, and the molar volume increases. With an increase in the molar fraction of aluminum chloride in the melt, an increase in the density and a decrease in the molar volume of the studied ionic liquid are observed due to an increase in the concentration of the heavier anion Al2Cl7– in comparison with the anion AlCl4–. The investigated ionic liquid was presented as a mixture of two salts: 1-butyl-3-methylimidazolium – AlCl4– (ionic liquid with a molar fraction of aluminum chloride equal to 0.5) and 1-butyl-3-methylimidazolium – Al2Cl7– (ionic liquid with a molar fraction of aluminum chloride equal to 0.67). For mixtures of these salts, the rule of additive addition of densities and molar volumes was proved, and the molar concentrations of ions present in the mixture were calculated. The dependence of the concentration of each ion both on temperature and on the molar fraction of aluminum chloride can be described by a linear dependence. With increasing temperature, the molar concentrations of each type of ions decrease due to an increase in the molar volume.
KEY WORDS:
chloraluminate ionic liquids, low-temperature melts, density, molar volume, molar concentration
DOI: 10.31857/S0235010620060055